feat(notify): release v1.8.0 — Slack/Teams/Google Chat/Telegram/webhook notifications

- Add internal/notify package: best-effort release notifications to Slack, Microsoft Teams, Google Chat, Telegram, and a generic JSON webhook; every target is independently opt-in and a failed notification never fails the release
- Add notify config section (slack_webhook_url, teams_webhook_url, google_chat_webhook_url, telegram_bot_token/telegram_chat_id, webhook_url) with matching env var fallbacks; 100% coverage plus FuzzMessagePayloads
- Wire notification sending into run() — fires after tag+push (including --no-release), skipped on --no-push/--no-commit since nothing was published yet
- Document the notify section in README, Hugo docs, and .releaser.yml template; update CLAUDE.md architecture/fuzzing tables
- Also commit the Apache License 2.0 docs-site footer link (docs/hugo.toml geekdocContentLicense), left uncommitted from a prior change

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/notify/notify_test.go

@@ -0,0 +1,137 @@
+package notify
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+// alwaysFailTransport returns an error for every request.
+type alwaysFailTransport struct{}
+
+func (alwaysFailTransport) RoundTrip(*http.Request) (*http.Response, error) {
+	return nil, &testTransportError{"connection refused"}
+}
+
+type testTransportError struct{ msg string }
+
+func (e *testTransportError) Error() string { return e.msg }
+
+func TestPostJSONSuccess(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	if err := postJSON(context.Background(), srv.URL, map[string]string{"a": "b"}); err != nil {
+		t.Fatalf("postJSON: %v", err)
+	}
+}
+
+func TestPostJSONBadURL(t *testing.T) {
+	err := postJSON(context.Background(), "http://\x00bad", map[string]string{"a": "b"})
+	if err == nil {
+		t.Fatal("expected error for invalid URL")
+	}
+}
+
+func TestPostJSONRequestFails(t *testing.T) {
+	orig := httpClient
+	httpClient = &http.Client{Transport: alwaysFailTransport{}}
+	defer func() { httpClient = orig }()
+
+	err := postJSON(context.Background(), "http://127.0.0.1:1", map[string]string{"a": "b"})
+	if err == nil {
+		t.Fatal("expected error when HTTP request fails")
+	}
+}
+
+func TestPostJSONNon2xx(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer srv.Close()
+
+	err := postJSON(context.Background(), srv.URL, map[string]string{"a": "b"})
+	if err == nil {
+		t.Fatal("expected error for 500 response")
+	}
+}
+
+func TestSendAllNoneConfigured(t *testing.T) {
+	errs := SendAll(context.Background(), Config{}, Message{Version: "v1.0.0"})
+	if errs != nil {
+		t.Fatalf("expected no errors, got %v", errs)
+	}
+}
+
+func TestSendAllAllSucceed(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	origBase := telegramAPIBase
+	telegramAPIBase = srv.URL
+	defer func() { telegramAPIBase = origBase }()
+
+	cfg := Config{
+		SlackWebhookURL:      srv.URL,
+		TeamsWebhookURL:      srv.URL,
+		GoogleChatWebhookURL: srv.URL,
+		TelegramBotToken:     "tok",
+		TelegramChatID:       "123",
+		WebhookURL:           srv.URL,
+	}
+	errs := SendAll(context.Background(), cfg, Message{Version: "v1.0.0", Notes: "notes"})
+	if errs != nil {
+		t.Fatalf("expected no errors, got %v", errs)
+	}
+}
+
+func TestSendAllAllFail(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer srv.Close()
+
+	origBase := telegramAPIBase
+	telegramAPIBase = srv.URL
+	defer func() { telegramAPIBase = origBase }()
+
+	cfg := Config{
+		SlackWebhookURL:      srv.URL,
+		TeamsWebhookURL:      srv.URL,
+		GoogleChatWebhookURL: srv.URL,
+		TelegramBotToken:     "tok",
+		TelegramChatID:       "123",
+		WebhookURL:           srv.URL,
+	}
+	errs := SendAll(context.Background(), cfg, Message{Version: "v1.0.0"})
+	if len(errs) != 5 {
+		t.Fatalf("expected 5 errors, got %d: %v", len(errs), errs)
+	}
+}
+
+func TestSendAllTelegramRequiresBothFields(t *testing.T) {
+	calls := 0
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		calls++
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	origBase := telegramAPIBase
+	telegramAPIBase = srv.URL
+	defer func() { telegramAPIBase = origBase }()
+
+	// Only bot token set — chat ID missing — Telegram target must be skipped.
+	errs := SendAll(context.Background(), Config{TelegramBotToken: "tok"}, Message{Version: "v1.0.0"})
+	if errs != nil {
+		t.Fatalf("expected no errors, got %v", errs)
+	}
+	if calls != 0 {
+		t.Fatalf("expected telegram to be skipped, got %d calls", calls)
+	}
+}